Arc tube system



Jan. 20; 1942. w p QVERBECK 2,270,601

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J 1942- w. P. OVERBECK 2,270,601

ARC TUBE SYSTEM Filed May 4, 1939 5 Sheets-Sheet 2 FIG. Z.

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FIG. 3.

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Jan. '20, 1942. w. P. QVERBECK 2,270,601

ARC TUBE SYSTEM Filed May 4, 1939 5 Sheets-Sheet 3 FIG. 5.

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W|Lcox E OVERBECK,

ATTY.

Jan. 20, 1942. w. P. OIVERBECK 2,270,601

ARC TUBE SYSTEM Filed May 4, 1939 5 Sheets-Sheet 4 FIG.

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5 Sheets-Sheet 5 INVENTOR.

Jan. 20, 1942. w. P. OVERBECK ARC TUBE SYSTEM 'Filed May 4, 1959 RESULTANT IDLE VOLTAGE ON leurrme Tulsa GRID W [I m P. G o m 7 R E T l 6E F E w Hm VPSG a .i All Kl n o E .v E N L G IDLE: VOLTAGE FR M ACROSS ARc TuaEs FIG ll lemTlNe 135E IDLE ANooE VOLTAGE Fle. l2.

Wn..cox I? OVERBECK, BY ATTY.

Patented Jan. 20, 1942' ARC TUBE SYSTEM Wilcox P. Overbeck, Waltham, Mass, assignor to Raytheon Manufacturing Company, Newton,

Mass., a corporation of Delaware Application May 4, 1939, Serial No. 271,679

19 Claims.

This invention relates to an arc tube system and more particularly to such a system in which two controlled arc tubes are connected reversely in order to supply a controlled alternating current load.

One of the main objects of this invention is to devise a simple and reliable firing circuit. It is desirable in such a firing circuit to have both tubes fail to conduct current upon the occurrence of any fault in the firing circuit. Particularly when using igniting electrodes of the type which are separated from a pool, cathode by an insu lating wall, it is desirable to impress substantially only positive impulses on the igniting electrade as described and claimed in the co-pending application of John W. Dawson, Serial No. 254,203, filed February 2, 1939, for an improvement in Arc discharge starting arrangement and method. It is further desirable to insure a reliable pickup of the are following each firing impulse substantially independent of load conditions. The objects of this invention also include satisfaction of each of the foregoing requirements. More particularly the present invention.

contemplates utilizing rapid change in the charge of the condenser to produce a short thing impulse. It also utilizes separate firing tubes which are each operated at their maximum effectiveness. The present invention also contemplates the provision of novel means for securing short firing impulses in the system under c'onsideration. The present invention also provides means for protecting the igniting electrodes of the arc tubes against excessive voltages.

The foregoing and other objects of this invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a diagrammatic representation of a circuit embodying the present invention;

Figs. 2 to 6 are curves illustrating the operation of the system shown in Fig. 1;

Fig. 7 is a vector diagram illustrating the relationships of the voltages impressed on the firing tubes of Fig; l;

Fig. 8- is a showing similar to Fig. 1 of another embodiment of this invention;

Figs. 9 and 10 are curves illustrating the operation of the system shown in Fig. 8;

Fig. 11 is a showing similar to Fig. 1 of still another embodiment of this invention; and

Fig. 12 contains curves illustrating the operation of the system shown in Fig. 11.

The embodiment illustrated in Fig. 1 consists of two are tubes I and 2 Tpreferably};f the mercury p001 cathode type. These tubescdntain mercury pool cathodes 3 and 4 andanodes 5 and 6, respectively, and are provided with igniting electrodes I and 8. Although these igniting electrodes may be of any type which initiates an are on the mercury pool cathode by means of an igniting impulse supplied thereto, they preferably are of the type which consists of a conductor separated from the mercury pool by an insulating layer which preferably consists of glass. More particularly these igniting electrodes may be of the form described and claimed in the copending application of Percy L. Spencer, Serial No. 259,355, filed March 2, 1939, for an improvement in Arc starting devices. In igniting electrodes of this kind, the glass layer on the igniting electrode conductor is in contact with the surface of the mercury pool, and the arc tends to form at some such point of contact. The upper ends of the electrodes 1 and 8 may be left exposed to the discharge space so as to provide discharge paths in parallel with the respective cathodes and igniting electrodes.

Two alternating current lines 9 and ID are connected to supply a suitable current alternating load which may consist of a transformer l I having a primary l2, a secondary I3-and a load II. In the particular system shown, the load I4 may consist of a resistance welding load. The are tubes L and 2 are interposed in one of the conductors It in order to control the flow of current to the load. In order to permit alternating current to flow through the tube system, the two tubes are reversely connected by means of the crossed conductors ['5 and I6. If the tubes I and 2 are conducting, current pulses of one polarity will flow through tube I and current pulses of the opposite polarity will flow through tube 2,

thus delivering alternating current to the load. If, however, tubes I and 2 are non-conducting, the load is deenergized.

Igniting transformers I! and I8 are provided to supply igniting impulses to the igniting electrodes 'I and 8, respectively. These igniting transformers are provided with secondary windings I9 and 20. The secondary winding I9 is connected between the igniting electrode 1 and the cathode pool 3, while the secondary 20 is connected between the igniting electrode 8 and the cathode pool I. The transformers I1 and I8 are also provided with primary windings 2| and 22 which are supplied with igniting voltage 1m ulses through a control circuit which is energized from a transformer 24 having a primary winding 25 energized with alternating current. This primary 25 may suitably be energized from the alternating current lines 9 and I0. The transformer 24 also has a secondary winding 25. The lower ends or the primary windings 2| and 22 are connected respectively by means of conductors 21 and 25 to the opposite sides of the secondary winding 26. The primary winding 2| is connected directly across the secondary winding 25 through a series circuit consisting of a resistance 29, a condenser 30, and a potentiometer 3| having a tap 35 thereon connected to the upper end of said primary winding 2|. The lower end of said potentiometer 3| is connected directly to the lower end oi! said primary winding 2|. Likewise the primary winding 22 is connected directly across the secondary winding 25 through resistance 32, a condenser 33, and a potentiometer 34. The potentiometer 34 likewise has an adjustable tap 35 leading to the upper end of the primary winding 22, the lower end of said potentiometer being directly connected to the lower end of said primary winding 22. The constants of the circuit described are so selected that the voltages supplied from the secondary winding 25 to the primary windings 2| and 22 through the series circuits traced above produce voltages in the secondary windings I3 and 20 which are insignificant as compared with the voltage necessary to ignite an arc in tubes I and 2. This is done by making the impedance of the condensers 30 and 33, at line frequency, high compared to the resultant impedances appearing across the terminals of the potentiometers 3| and 34.

In order to produce surges of current through the primary windings 2| and 22 so as to produce the requisite firing impulses, the system is supplied with two controlled gaseous discharge tubes 31 and 33. These tubes are preferably of the type in which a grid determines the initiation of an ionizing discharge therein but which thereafter during the period of conduction loses control of the discharge. The tubes 31 and 38 are provided with thermionic filamentary cathodes 33 and 40, anodes 4| and 42, and control grids 43 and 44. The secondary winding 25 is provided with a center tap which is connected directly to the cathodes 3B and 40. A switch 45 may be interposed in this connection, whereby the system may be turned on and oil. The anodes 4| and 42 are connected directly to the upper ends of the resistances 23 and 32, respectively.

In order to cause the tubes 31 and 38 to start conducting at the proper time, impulses are supplied to the grids 43 and 44, as will be described below, from a potentiometer 41 which is connected directly across the arc tubes and 2. The potentiometer 41 is provided with a center tap 43 and two taps 49 and 50 on either side of said center tap. The tap 49 is connected through a high resistance to the grid 43, while the tap 55 is likewise connected through a high resistance 52 to the grid 44. The resistances 5| and 52 may be of the order or 100,000 ohms each. The use of these high resistances tend to make the grids 43 and 44 sensitive to outside disturbances, and in order to decrease this tendency, condensers 53 and 54 are preferably connected between the grids and cathodes 43 and 33, and 44 and 40, of the tubes 31 and 38, respectively.

In addition to the impulses supplied from the potentiometer 41, the grids 43 and 44 are supplied with a direct current bias from a suitable source of direct current. As illustrated in Fig. 1. this source of direct current may consist of a rectifier arrangement, including a rectifier tube 55 having a filamentary cathode 55, and a pair of anodes 51. The two anodes 51 are connected to opposite sides of a secondary winding 53 which may be suitably provided on the transformer 24. The secondary winding 58 is provided with a center tap 53 which leads directly to a center tap on a bias control resistance 5|. The filamentary cathodes 39, 40 and may all suitably be supplied with heating current from another secondary winding 52, also provided on the transiormer 24. One end of the resistance 5| is connected directly to a center tap 63 on the secondary winding 62, and thus to the cathode 55 oi rectifier tube 55. Thus the direct current output of said rectifier tube is connected directly across the left half: of said resistance 5|. In order to connect the direct current supplied by the rectiher 55 into the circuits of the grids 43 and 44, a conductor 64 extends from the right-hand end of the resistance Bl to the center tap 48 on the potentiometer 41. This interposes into the circuits of the grids 43 and 44 sufilclent negative bias so that the impulses supplied to said grids from the potentiometer 41. are insufilcient to initiate a discharge in the tubes 31 and 33, respectively. In order to decrease this bias sufllciently to enable the system to be set in operation, a conductor 65 extends from a tap on the left half of the resistance 6| through a pair of control contacts 66 to the right-hand end of the resistance 5|. When the control contacts 66 are closed, the potential of the left-hand tap on resistance 6| is supplied as the bias to the grids 43 and 44. This potential has a lower negative value than the potential supplied to said grids when the control contacts 65 are open. A condenser 51 connected across the output of the rectifier tube 55 may be provided in order to filter the direct current output thereof.

In are devices of the type represented by tubes and 2, the firing impulses supplied to the igniting electrodes 1 and 8 produce incipient arc spots on the surface of the mercury pools 3 and arc.

4. In order, however, for said incipient arc spots to progress into true arcs, it is desirable for the current drawn from said incipient arc spot to rise rapidly to a value sufiicient to sustain a true In many cases the nature of the load impressed on the arc tubes is such that its current requirements upon the creation of incipient arc spots do not rise at a sufllciently rapid rate to transfer said incipient are spots into true arcs. Such a condition results in erratic operation of tubes and 2. In order to eliminate this defect, an auxiliary circuit which insures, the proper rate of current rise through the tubes and 2, independently of the characteristics of the load circuit in the particular system shown, is provided. This auxiliary circuit consists of a condenser 68 and a resistance 69 connected directly across the load. In a particular instance where the line voltage was 500 volts, the resistance 59 was ohms and the condenser 59 was one microfarad. Of course these values may be varied to 'suit the particular conditions which may be me In arc tubes of the type involved herein, it is desirable that the maximum value or the igniting voltage impulses supplied to the igniting electrodes 1 and 8 be restricted to substantially a predetermined value in order to prevent damage to said igniting electrodes. This protection is. afforded in the present arrangement by a spark gap III connected between each igniting electrode and its associated cathode pool.

The operation of the system described above can be better understood by referring to the curves shown in Figs. 2 to 6, inclusive. These curves do not purport to show quantitatively the currents and voltages involved. However, they do represent in a general qualitative manner the true operation of the system. In Fig. 2 the sine wave a represents the line voltage which appears across the conductors 8 and Ill. The curve b represents the load current flowing to the primary I2. In the systems which are contemplated, particularly the resistance welding systerns, the current b lags the voltage a, and in the particular instance shown, this lag is about 60 degrees. As the current passes through zero, one of the arc tubes I or 2 goes out, and it is desirable that the other tube start immediately in order to deliver smooth alternating current to the load. The curve 0 which represents the voltage across the tubes I and 2 shows that when one of the are tubes goes out, the voltage across said tubes immediately rises to the instantaneous value of the line voltage at that particular moment. The system is so arranged that this voltage impulse sets the firing circuit in operation so as to ignite the previously idle tube which thereupon immediately starts conducting current so that the voltage across the tubes then drops to the relatively low value of the tube are drop. This operation takessuch a short time that the rise in voltage across the tubes lasts for a very short time, and therefore these voltage impulses are represented in curve c by vertical lines. Of course it is to be understood that this change does occupy some time interval; which, however, it is impractical to. illustrate in Fig. 2. It will be seen, therefore, that the voltage across the tubes I and 2 supplies voltage impulses at exactly the right momentsin order to alternately fire the tubes I and 2 so as to cause the alternating load current b to flow smoothly through said tubes. The potentiometer 41, which is connected directly across the tubes I and 2, hasthis voltage wave 0 impressed upon it. By means of the taps 49 and 50, this voltage wave is impressed upon the grids 43 and 44 of the tubes 31 and 38. By properly adjusting the position of the taps 49 and 50, the magnitudeof the voltage impulses thus supplied to these grids may be adjusted to the desired value.

The manner in which the voltage impulses derived from the taps 43 and 50 controls the initiation of conduction in the tubes 31 and 38 will be described in connection with Fig 3.

Here again the line voltage is represented by the curve a. The voltage which is supplied to the anode of one of the tubes 31 or 38 during the time when no conduction occurs is represented by the sine wave d. As will be explained below, the phase angle of the voltage d is so adjusted that the voltage impulses derived from the potentiometer 4'! occur at th maximum value of the voltage d. In this analysis it is assumed that the tubes 31 and 38 start conducting current whenever the grids 43 and 44 become positive. This is a sufliciently accurate assumption for our present purposes. The direct current bias which is impressed on thegrids 43 and 44 with the control contacts 63 closed is represented by the dotted line e. Superimposed on this bias is the voltage I which represents that portion of the voltage 0 of Fig. 2 which is sitions of the taps 49 and 50 provide means for applied to the respective tube under consideration through thetap 43' or 58. The values of the voltages e and j are so relatedthat the positive peaks of 1 cause the associated grid to become positive, and thus the associated tube 31 or 38 flres at the instant when the peaks of the voltage wave J occur. Upon the initial starting of the system, it will be understood that the peaks of. voltages c and I do not occur but the corresponding voltages rise 'along asine wave variation substantially as represented by the line voltage to substantially the same value as that represented by the magnitude of said peaks of c and 1. Thus upon the initial closing of the contacts 36, the grid on the first tube 31 or 38 to fire will reach a positive value at substantially the same instant as that represented by the peaks of the voltage f. In this way the initial ignition of the tubes I or ,2 occurs substantially at the instant when the current to the load naturally tends to start from zero. This operation eliminates undesirable surges of current through the load which otherwise mightoccur. It will further be seen that adjustment of the bias volt age e by shifting the tap on resistance 6| and the adjustment of voltage I by varying the poadjusting this initial point of firing of the tubes I and 2. Due to the position of the taps 49 and 50 on opposite sides of the center tap 48 of the I potentiometer 41, the grids 43 and 44 become alternately positive upon alternate impulses of the voltage I. Thus when the anode 6 becomes positive and positive voltage impulse is supplied to the grid 44, the tube 38 starts conducting current which in turn fires the associated tube 2. Likewise when anode 5 becomes positive, the grid 43 becomes positive and the tube 31 starts conducting current which flres tube I. Upon opening the control contacts 66, the direct current bias on the grids 43 and 44 increases to the value represented by the dotted line g. The bias 9 is sufficient so that the peak values of voltage f never are sufllcient to cause the grids 43 and 44 to become positive, and thus tubes 31 and 38 do not conduct current and the tubes I and 2 remain deenergized. In Fig. 3 there is also represented by the sine wave h the voltage which appears across one of the condensers 30 or 33 during this idle period. The manner in which the phase relationship shown occurs will be described later. e

The manner in which the start of conduction in tubes 31 and 38 produces firing impulses on the igniting electrodes will be explained in connection with Figs. 4 and 5. In Fig. 4 the curve a and the dotted curves d and h have the same significance as the corresponding curves in Fig. 3. The curve 1', however, represents the anode voltage of one of tubes 31 or 38 during the enerrgized period of the system. It will be seen that when the tube under consideration starts conducting current, the voltage across it drops to the relatively low value of the tube drop. Said igniting tube, however, conducts for but a short period until the current through it tends to reverse, whereupon th tube goes out and the voltage reverses and gradually approaches the sine wave variation of its idle state. Thereupon it is again ignited and the voltage variation is repeated. The curve is represents the voltage variations on one of the associated condensers, for example 30, which occurs during such energized period. When the associated tube 31 starts conducting current. this in effect connects the left-hand side of condenser 38 directly to the center tap 45, and thus produces a sudden change in the voltage impressed upon the condenser. This sudden change occurs immediately upon-the start of conduction of said tube 31.

The voltage variation on the condenser then proceeds in a more gradual way, as represented by said curve It. In Fig. the condenser voltage curve It is reproduced in dotted form. The curve 1 represents the current which flows through the associated condenser upon being supplied with the voltage wave k. Since the voltag which a condenser can assume depends upon the quantity of electricity supplied thereto, a rapid change in voltage on the condenser will produce a large current flow during such period of rapid change. Thus the curve 1 shows very large peaks at the instant when the associated tube 31 or 38 starts conducting current which, as described above, produces thesudden change in the voltage impressed on the associated condenser 38 or 33. The slower variations in the condenser voltage produce smaller values of the current wave 1 which progress above and below the zero axis. In actual practice the values of the peaks of curve 1 are so large as compared with the rest of said curve that these peaks have been shown greatly reduced in size in Fig. 5 in order to illustrate the actioninvolved. This is due to the fact that the impedances of the condensers 38 and 33 to the high frequency components represented by the discontinuity in the voltage wave k are low compared to the resultant impedances across the potentiometers 3| and 34 to these high frequency components. Also the unidirectional character of the peaks in the condenser current 'is due to the fact that the equivalent circuit across each igniting electrode and cathode is non-oscillatory due to the presence of the resistive component in said equivalent circuit which is of a sufllcient value to supply at least critical damping to said equivalent circuit. This resistive component may be due either to resistances 3| and 34 or to any other suitable resistive component, such as the occurrence of a discharge in the discharge spaces'between the cathodes 3 and 4 and the exposed portions of the electrodes 1 and 8, respectively. In the latter case it may be possible to eliminate the resistances 3| and 34. Thus it will be seen that the circuit of Fig. 1 produces substantially solely unidirectional current impulses through the condensers 38 and 33 which are of very short time duration. These currents flowing through the potentiometers 3| and 34 produce a voltage across the said potentiometers which is substantially identical in form with the curve 1. The desired portion of this voltage impressed on the primary windings 2| and 22 produces a corresponding voltage wave in the secondary windings l9 and 28. The ratio of transformation ofthe transformers l1 and i8 is such as to cause the secondary windings l3 and 28 to deliver high voltage impulses to the igniting electrodes 1 and 3 at the peaks of the curve 1, which high voltage impulses are sufiicient to initiate arcs on the cathodes 3 and 4, respectively. Adjustment of the taps 35 and 38 will adjust the value of these igniting voltage impulses. The polarities of the secondary windings l8 and 28 are arranged so that the unidirectional igniting voltage surges applied to the igniting electrodes 1 and 8 make these igniting electrodes positive with respect to their associated cathodes 3 and 4, respectively.

Therefore these igniting electrodes are supplied with substantially exclusively positive igniting impulses. This type of ignition results in long life for the igniting electrodes, as more fully described in said co-pending application of John W. Dawson, Serial No. 254,203. I

As previously discussed in connection with Fig.

4, tubes 31 and 38 are caused to start conduction of current at the maximum values of the voltage supplied to the anodes 4| and 42, respectively. By firing the tubes 31 and 33 at these points, the maximum variation of the voltages on the condensers 38 and 33 respectively is produced, and thus the maximum value of the igniting voltage surges is likewise produced. Conversely by firing the tubes 31 and 38 so as to give such maximum igniting voltages, tubes 31 and 38 can be a minimum size to produce a desired magnitude of igniting voltage. The manner in which the ignition of the tubes 31 and 38 is caused to occur at the desired time can be best understood by referring to the vector diagramofFia 'l. Let us consider one of the tubes 31. In Fig. TEt represents the voltage across the entire secondary winding 26. Et/Z represents the voltage across the lefthand half of said secondary winding. I represents the current flowing across the entire secondary winding 26. The effect on this series circult of the potentiometer 3| and the transformer l1 connected across it is negligible in so far as the current I is concerned, and therefore the series circuit under analysis has been considered as consisting solely of the resistance 28 and the condenser 38 in series. Due to the capacity of the condenser 38, the current I leads the voltage Er. IR represents the voltage drop across the resistance 29. 1X0 represents the voltage drop across the condenser 38. These last two vectors are drawn reverse in direction, and therefore have a minus sign. The vectors IR and Die must necessarily be so related that their vectorial sum is equal to the voltage Er. However, the vector EA, which represents the voltage between the cathode 39 and the anode 4|, extends from the end of the vector Ec/2 to the intersection of the vectors IXc andIR. The vector EA likewise is drawn reverse in direction, and therefore has a negative sign. It will be seen that by adjusting the values of the resistance 23 and the condenser 38, the vectors IXc and IR can be adjusted so as to give to the vector EA any desired phase relationship with respect to the voltage Et. In the arrangement shown in Fig. 1, Et of course is also directly in phase with the voltage across the lines 8 and i8. In Fig. '1 EA is shown as having a suflicient angle of lead with respect to the voltage Et tocause the firing impulses supplied to the tube 31 to occur at the peak of said volta e EA. If the point of firing, however, were to shift as, for example, by changing the type of load on the system, the resistance 29 and condenser 38 could be adjusted with respect to each other'so as to produce a difierent phase relationship between the voltages EA and E1; in order to again cause the firing of tube 31 to occur at the peak value of its anode voltage. In Fig. 1, for the purposes of such adjustment. the resistance 28 is shown as being adjustable.

As previously indicated, the condenser 88 and resistance 69 connected across the load circuit insure a reliable pickup of the arcs in tubes and 2 upon the occurrence of the igniting impulses. The operation of this portion of the system will be best understood by referring to Fig. 6. In this figure the curve a has the same significance ask-20,001

as previously described, namelyithe iine voltage. The curve m represents the current flowing through one of the arc tubes I or 2, When an igniting impulse is supplied to the arc tube at the firing point, the discharge tends to start, causing-the voltage across the tube to fall to a comparatively low value, thus impressing across the series circuit, consisting of the condensers 88 stead of charging the condensers 30 and 33 through resistances 23, as in Fig. 1, these; conincipient are spot on the cathode-pool to a true are spot. The-charging current flowing through said series circuit tends to persist for a time sufflcient to maintain this current at the requisite value until the load current has risen to the same value, whereupon said load current takes over the function of maintaining the are spot. The dotted portion 11. represents the variation in the load current from the firing point. It will be seen that the rate of rise of this portion of the load current curve is very much less than that, due to the series condenser and resistance circuit. Due to the short period during which the igniting impulse is present, in many instances this rate of rise of the load current would not be suilicient to transfer the incipient arc spot into a true are spot, during said short igniting interval. The rate of rise of the current through the series condenser and resistance circuit, however, is sufilcient to accomplish this result.

densers are each connected through the tubes 31 and 38, respectively, across opposite. halves of the secondary winding 28. A resistance II is connected across the condenser and potentiometer 3| in series. Likewise a resistance I2 is connected across the condenser 33 and resistance 34 in series. The resistances 'II and I2 are of a value to cause the condensers 30 and 33 to become substantially discharged during one alternation' of the alternating current.

Instead of having the resistance 63 and condenser 68 connected across the load as'in Fig. 1, these elements could be connected in series across the tubes I and 2. In this way the voltage of the source charges the condenser 68 to a substantial value before the tubes I and 2 fire. Thus when the tubes I and 2 do fire, the energy of the condenser is supplied immediately to the respective tube to produce the initial surge of current which transfers the incipient are spot into a true are spot, and maintains it until the loadcurrent reaches the requisite value as explained above in connection with Fig. 6.

The operation of Fig. 8 follows very closely that of Fig. 1, except for the manner in which the voltages across the condensers 30 and 33 are subjected to a rapid variation. This feature will be best understood by reference to Figs. 9 and 10.

. In Fig. 9 the curve m represents the line voltage.

In the system described above, with the switch i 46 in its closed position, the system is set in operation by closing the contacts 66. As long as said contacts are closed, alternating current is supplied to the load I4. As soon as the contacts and no current is supplied to said load. Since the load is an alternating current device, it is desirable not to supply direct current thereto. Therefore, if the firing circuit fails to supply an igniting impulse to one are tube, it is desirable that said circuit should likewise fail to supply an igniting impulse to the other are tube. The present arrangement accomplishes this result in substantially all instances. Thus if something happens to the rectifier system and the direct current bias is removed from the grids 43 and 44, the tubes 31 and 38 will start conducting current at substantially the zero point of the anode voltage in each case. Firing at this point will, however, produce a minimum change in voltage on the condensers 30 and 33 as contrasted with the maximum change which occurs when the tubes 31 and 38 fire at their maximum anode voltage. This minimum change in condenser voltage does not produce a sufficient surge of current to result in a voltage impulse supplied to the corresponding igniting transformer to cause ignition of the corresponding arc tube. Therefore the tubes I and 2 under these conditions will not be ignited. Various other defects which might possibly occur in the firing circuit likewise will fail to ignite both tubes I and 2.

Other systems than those in accordance with Fig. 1 may be devised, utilizing various aspects of the present invention. Such an alternative system is shown in Fig. 8. In this figure the same reference numerals are applied to elements identical with those shown in Fig. 1. In Fig. 8, in-

- 66 are opened, thetubes I and 2 are deenergized,

Since there are no phase shift means on the anodes of the tubes 31 and 38, as provided in Fig. 1, the voltage on these anodes during an idle period likewise follows the curve m. Also since the firing point is fixed by the load current, as previously described in connection with Fig. 2, the tubes 31 and 38 of Fig. 8 are not fired at the maximum value of the anode voltage. For this and other reasons Fig. 1 represents the preferred embodiment of my invention. In Fig. 9 -the curve n represents the anode voltage of one of the tubes 31 and 38 during an active period. When the igniting tube is fired, the voltage across it falls to the relatively low value of the tube drop. The igniting tube then conducts for a short time. However, due to the tendency of the current fed to the condenser 30 or 33 to lead the voltage, said current soon tends to reverse and the igniting tube goes out. This anode voltage then follows the solid portion of curve n below the axis, and gradually tends back to the original sine wave variation. In Fig. 10 the curve 0 represents the condenser voltage. It will be seen that there is no voltage on the condenser until the igniting tube fires. When this occurs the condenser is subjected to the sudden application of the voltage at that point which exists across the associated half of the secondary winding 26. The condenser voltage follows this secondary voltage until the point z where the igniting tube goes out. Thereupon the condenser discharges through its associated resistance II or 12 until it is entirely discharged. As previously indicated, this discharge occurs prior to the next ignition of said igniting tube. The curve 1) represents the condenser current. As previously described, the sudden voltage variation applied to the condenser causes a large surge of current, as represented by the vertical lines of curve p. The slower variation of the condenser voltage thereafter produces I a relatively small, current passing above and bethe arc tubes I or 2. Likewise it will be'seen that this igniting voltage is substantially unidirectional. As in the case of Fig. 1, these unidirec- ,tional impulses are so arranged that the igniting electrodes I8 are supplied with substantially solely positive igniting impulses.

Instead of utilizing a D. C.- bias on the grids oi tubes 31 and 38 to secure the proper firing of these tubes, 9. phase-shifted bias could be used as illustrated in Fig. 11. This figure represents asystem substantially the same as that illustrated in Fig. 1, and the same reference numerals are applied to elements identical with those shown in Fig. 1. In Fig. 11 a phase-shifted bias is impressed on the grids 43 and 44 of tubes 31 and 38 from a phase-shift circuit consisting of a secondary winding 13 on the transi'ormer 24, having a resistor I4 and a condenser I connected in series across the ends of said secondary winding 13. A resistance 15 is connected from the point between the resistor "I4 and condenser 15 to a center tap 18.0n the secondary winding 13. The resistor 14 may be provided with an adjustment in order to fix the desired phase angle of the voltage appearing across the resistance 18. A center tap TI on the resistance IE is connected to the center tap 83 on the cathode-heating secondary winding 62. The upper end of the resistance 16 is connected by means of a circuit 13 to the grid 43, while the lower end of said resistance 16 is connected through a circuit 80 to the grid 44. Instead of taking the voltage across the tubes I and 2 from a potentiometer as in the case of Fig. 1, a transformer BI is connected across said tubes in Fig. 11. The transformer 8| has a primary winding 82 connected between the crossed conductors I5 and I 6 and the tip of secondary windings 83 and 84. The secondary winding 83 is interposed in the circuit 19 of the grid 43, while the secondary winding 84 is interposed in the circuit 88 of the grid 44. In this way the voltage from across the tubes I and 2 is superimposed on the A. C. bias supplied to the grids 43 and 44 from the phase-shifting network described above.

Instead of starting and stopping the operation of the system by control contacts in the grid circuits of the tubes 31, 38, as in the case of Fig. 1, the system of Fig. 11 utilizes control contacts 85 connected in the common anode lead from the center tap 45 to the tubes 31 and 38. By closing the control contacts 85, the anode circuits of these tubes-are closed, and by opening said control contacts, these anode circuits are open, and the system is deenergized. It is sometimes desirable to connect condensers 86 across the two halves of the secondary winding 28 in order to prevent a drop in the voltage upon the firing of the tubes 31 and 38. This expedient can also be utilized in the other systems heretofore described.

The operation of Fig. 11 follows very closely that of Fig, 1, except for the manner in which the voltages supplied to the grids 43 and 44 vary during the various phases of operation. This feature will be best understood by reference to Fig. 12. In this figure the curve a represents the line voltage and the curve d represents the idle anode voltage of one of the igniting tubes, for example tube 31. These are the same voltages which have previously been represented in Figs. 2 to 4. The A. C. bias voltage derived from the phaseshift circuit and supplied to the grid 43 of the tube 31 is represented bythe curve E. The voltage appearing across the secondary winding 83 during the idle condition of the system is represented by the curve Ea in phase with the line voltage a. The sum of the voltages Ea and E5 is represented by the curve E The voltage E is the voltage which appears on the grid 43 during the idle condition of the system. Therefore when the control contacts are closed, the associated arc tube I will be ignited by the voltage Eg at the first firing point indicated in Fig. 12. Upon the ignition of said tube, the voltage across it substantially disappears, and therefore the resultant voltage on the grid 43 will follow substantiallyalong the curve Es. Upon the extinction of the tube I and the ignition of tube 2 at the middle firing point indicated in Fig. 12, the voltage on the grid 43 will shift suddenly to the voltage of the curve E3, but since this occurs during the non-conducting half of the tube 31, no change in its operation takes place. Upon ignition of the tube 2, the voltage on the grid 43 again follows the curve E3 until the third firing point is reached. At this point the arc tube 2 is extinguished and the voltage on the grid 43 rises suddenly from the curve E5 to the curve E thus causing the tube 31 to fire at that point, and giving to the tube I an igniting impulse which ignites the tube I and starts the cycle of operation over again. It will be seen that in this embodiment likewise the voltage across the tubes I and 2 supplies impulses to the grids 43 and 44 which accurately determine the time at which each of said are tubes I and 2 are ignited. The actual mechanism of the derivation of an igniting impulse from the firing of tubes 31 and 38 is identical with that described in connection with Figs. 1 to 7, inclusive.

Of course it is to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electric control system comprising a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, and means responsive to the voltage of said source appearing across said are discharge devices whenever the current through said discharge devices drops to zero for supplying an igniting impulse to one of said igniting electrodes whenever the current through the arc discharge device associated with the other of said igniting electrodes drops to zero.

2. An electric control system comprising a load circuit, circuit means for connecting said load circuit to a source of alternating current, said load circuit having a power factor less than per cent., a pair of inversely connected are discharge devices interposed in said circuit means for controlling the flow of current of said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, and means responsive to the voltage of said source appearing across said arc discharge devices whenever the current through said discharge devices drops to zero for supplying an igniting impulse to one of said igniting electrodes whenever the current through the arc discharge device associatedwith the other said igniting electrodes drops to zero.

3. An electric control ystem comprising a load circuit, circuit means or connecting said load circuit to a source of alternating current, said load circuit having a lagging power factor, a pair of inversely connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load'circuit, each of said are discharge devices comprising an anode, a

pool type are cathode, and an igniting electrode,

separated from said cathode by an insulating wall in contact with said cathode pool for'initiating an are on said cathode pool, and means responsive to the voltage of said source appearing across said are discharge devices whenever the current through said discharge devices drops to zero for supplying an igniting impulse to one of said igniting electrodes whenever the current through the arc discharge device associated with the other of said igniting electrodes drops to zero.

4. An electric control system comprising a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, a circuit for supplying igniting impulses to said igniting electrodes including a condenser asso-' to the condenser associated with one of said ig-- niting electrodes whenever the current through the arc discharge device associated with the other of said igniting electrodes drops to zero, whereby a current surge flows in said condenser and supplies an igniting impulse to said associated igniting electrode.

. In combination, an electrical discharge device comprising at least two principal electrodes,

and a control electrode for rendering said dis charge device conductive, a condenser, a resistance, circuit means for supplying said condenser and resistance with alternating current by connecting said condenser andresistance in series with an alternating current source, a controlled rectifier connected from a point between said condenser and resistance to an' intermediate voltage of said source, means for firing said rectifier at a point substantially delayed beyond the beginning of the positive half of the voltage wave applied to said rectifier, whereby a surge of current is produced through said condenser, and means responsive to said current surge for transmitting an impulse to said control electrode for rendering said discharge device conductive.

6. In combination, an electrical discharge device comprising at least two principal electrodes, and a control electrode for rendering said discharge device conductive, a condenser, a resistance, circuit means for' supplying said condenser and resistance with alternating current by connecting said condenser and resistan'cein series with an alternating current source, a controlled rectifier connected from a point between said condenser and resistance to an intermediate voltage of said source, means for firing said rectifier at substantially the maximum positive value of the alternating voltage impressed on said rectifier, whereby a surge of current is produced through said condenser, and means responsive to said current surge for transmitting an impulse to said control electrode for rendering said discharge device conductive.

7. In combination, an electrical discharge device comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cath'ode pool for initiating an arc on said cathode pool, a circuit for supplying. igniting impulses to said igniting electrode including a condenser associated with said igniting electrode and adapted to besupplied with current from a source of potential, means for suddenly changing the voltage supplied to said condenser, whereby a current surge flows in said condenser and supplies an igniting impulse to said associated igniting electrode, and said circuit having a resistive impedance in said circuit of a suincient value so that the circuit between said igniting electrode and said cathode is non-oscillatory, whereby said igniting impulse is substantially unidirectional.

8. In combination, an electrical discharge decondenser, whereby a current surge flows in said.

condenser and supplies an igniting impulse to said associated igniting electrode, said circuit comprising a closed circuit around said condenser and having a resistive impedance in said circuit of a sufiicient value so that the circuit between said igniting electrode and said cathode is non-oscillatory, whereby said igniting impulse is substantially unidirectional,

9. In combination, an electrical discharge device comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, a circuit for supplying igniting impulses to said igniting electrode including a condenser and a transformer in series and adapted to be supplied with current from a source of potential, the output of said transformer being supplied to said igniting electrode, means for suddenly changing the voltage supplied to said series circuit, whereby a current surge flows in said condenser and supplies an igniting impulse to said associated igniting electrode, and a resistive impedance across said transformer, whereby said igniting impulse is substantially unidirectional.

10. In combination, an electrical discharge device comprising .an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, a circuit for supplying ignitlng impulses to said igniting electrode, including a condenser and a transformer in series and adapted to be supplied with current from an alternating current source, the output of said transformer being supplied to said igniting electrode, means for suddenly changing the voltage supplied to said series circuit, whereby a current surge flows in said condenser and supplies an igniting impulse to said associated igniting electrode, and a resistive impedance across said transformer, whereby said igniting impulse is substantially unidirectional.

11. An electric control system comprising a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely connected are discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode for initiating an are on said cathode pool, a controlled gaseous discharge tube for each arc discharge device for supplying igniting impulses to the associated igniting electrode, each of said controlled gaseous discharge tubes comprising an anode, a cathode, and control means for determining the firing point of its associated controlled gaseous discharge tube, means for connecting a source of voltage to each last-named cathode and anode, and means for supplying firing impulses from the voltage appearing across said arc discharge devices to each of said control means.

12. An electric control system comprising a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode for initiating an are on said cathode pool, a controlled gaseous discharge tube for each arc discharge device for supplying igniting impulses to the associated igniting electrode, each of said controlled gaseous discharge tubes comprising an anode, a cathode, and control means for determining the firing point of its associated controlled gaseous discharge tube, means for connecting a source of voltage to each last-named cathode and anode, means for supplying firing impulses from the voltage appearing across said are discharge devices to each of said control means, and means for impressing a bias voltage on each of said control means to cause said controlled gaseous discharge tubes initially to fire at a predetermined point.

13. In combination, a load circuit, circuit means for connecting said load circuit to a source of current, an arc discharge device interposed in said circuit means for controlling the flow of current to said load circuit, said are discharge device comprising an anode, a pool type are cathode, and an igniting electrode for initiating an are on said cathode pool, means for supplying igniting impulses to said igniting electrode, and an auxiliary circuit connected to the output of said are discharge device, com- 14. In combination, a load circuit, circuit means for connecting said load circuit to a source of current, an arc discharge device interposed in said circuit means for controlling the flow of current to said load circuit, said are discharge device comprising an anode, a pool type are cathode, and an igniting electrode for initiating an are on said cathode pool, means for supplying igniting impulses to said igniting electrode, and an auxiliary circuit connected in parallel with the load circuit comprising a resistance and a condenser in series, said condenser being sufficiently large and said resistance being sufficiently small to produce a starting current surge of sufiicient value to establish an are spot on said cathode when said igniting electrode is supplied with an igniting impulse.

15. In combination, a load circuit, circuit means for connecting said load circuit to a source of current, an arc discharge device interposed in said circuit means for controlling the flow of current to said load circuit, said are discharge device comprising an anode, a pool type are cathode, and an igniting electrode for initiating an arc on said cathode pool, means for supplying igniting impulses to said igniting electrode, and an auxiliary circuit connected across said are discharge device, comprising a resistance and a condenser in series, said condenser being suiiiciently large and said resistance being sufhciently small to produce a starting current surge of suflicient value to establish an arc spot on said cathode when said igniting electrode is supplied with an igniting impulse.

16. In combination, a load circuit, circuit means for connecting said load circuit to a source of current, an arc discharge device interposed in said circuit means for controlling the flow of current to said load circuit, said are discharge device comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall in contact with said cathode pool for initiating an are on said cathode pool, means for supplying igniting voltage impulses between said igniting electrode and cathode, and a discharge gap across said igniting electrode and cathode to break down upon the application of an excessive igniting voltage for protecting said insulating wall from excessive igniting voltages,

1'1. A control system comprising a load circuit, means for connecting said load circuit to a source of current, a discharge device interposed in said means for controlling the flow of current to said load circuit, said discharge device comprising an anode, a pool type are cathode, and an igniting electrode for initiating an are spot on said cathode, means for supplying an ig niting impulse to said igniting electrode, and an auxiliary circuit including a condenser connected in said system to feed energy between said cathode and anode, said condenser being sufliciently large and the impedance of said auxiliary circuit to current surges being sufiiciently small to produce a starting current surge between said cathode and anode of suflicient magnitude to establish an are spot on said cathode upon said igniting electrode being supplied with an igniting impulse.

18. A control system comprising a load circuit, means for connecting said load circuit to a source of current, a discharge device comprising an anode and a pool type are cathode interposed in said means for controlling the flow of current to said load circuit, said discharge device also comprising an igniting electrode for initiating an arc spot on said cathode, means for supplying an igniting impulse to said igniting electrode, and an auxiliary circuit including a condenser connected in said system to feed energy between said cathode and anode, said condenser being sufiiciently large and the impedance of said auxiliary circuit to current surges being sufllciently small to produce a starting current surge between said cathode and anode of sufficient magnitude to establishan arc spot on said cathode upon said igniting electrode being supplied with an igniting impulse.

19. A control system comprising a load circuit, means for connecting said load circuit to a source of current, a discharge device comprising an anode and a pool type are cathode interposed in said means for controlling the flow of current to said load circuit, said discharge device also comprising an igniting electrode for initiating an are spot on said cathode, means for supplying an igniting impulse to said ignifing electrode, and an auxiliary circuit including an electrical energy storage reservoir means connected in said system to feed energy between said cathode and anode, said reservoir means being sufilciently large and the impedance of said auxiliary circuit to current surges being sufllciently small to produce a starting current surge between said cathode and anode of sufficient; magnitude to establish an are spot on said cathode upon said igniting electrode being supplied with an igniting impulse. I

WILCOX P. OVERBECK. 

